An AU spokeswoman has said the organisation was "frankly alarmed" by the comments, and a number of African nations have spoken out or summoned US diplomats to explain.

Rex Tillerson.

Mr Trump’s letter, seen by The Associated Press and confirmed by two US officials, says the US "profoundly respects" the partnerships and values shared by the US and Africans and that the president’s commitment to strong relationships with African nations is "firm".

The letter offers President Trump’s "deepest compliments" to the African leaders as they gather.

It notes that US soldiers are "fighting side by side" against extremism on the continent and that the US is working to increase "free, fair and reciprocal trade" with African countries and partnering to "safeguard legal immigration".